The Addiction Severity Index (ASI) is probably the most used assessment instrument in the substance abuse field. However, a number of significant changes have taken place in the field since the instruments developed 20 years ago and research has revealed some limitations in some of its summary indices, which are used to describe patient background and recent status. There is therefore a need to revise the ASI to strengthen its coverage of important areas and to enhance structural integrity. The proposed research represents such an undertaking. In the Development stage of the project the domains will be reconceptualized and items added and preliminary tested for psychometric integrity and understandability. This preliminary work will be undertaken by our Center's ASI working group with the consultation of two external advisory panels, patient respondent queries, review of pertinent literature, and other extant instruments. Once a preliminary instrument is developed, consisting of both a background component characterizing lifetime problem severity and a monitoring component describing recent problems, interviewers will be trained and the instrument will be administered in the Pilot stage at treatment intake to a diverse sample of 400 substance dependence patients/clients. The monitoring component will be re-administered at six months. This work should yield a viable instrument with items found to be psychometrically sound. The third, Final Testing stage of the project will include establishing the structural integrity, generalizability (primary substance dependence groups and sociodemographic subgroups), norming and computerizing scoring of the two instrument components, establishing test-retest reliability, and concurrent and predictive validity of the two components, and a small study of the concurrent validity of a set of cost items in) integrated into the instrument (in collaboration with Center Project 4). The stage 3 participant sample will consist of 1100 patients/clients at intake (200 primary cocaine dependent, 220 primary opioid dependent, 220 primary alcohol dependent, 220 welfare to work, and 220 drug court) who will be administered the full instrument at treatment intake. An external validation battery will be administered to half of the patients in each of designated subgroups at intake. At six months, 1000 patients/clients will be re-administered the monitoring component at month outcome and several other outcome measures will be obtained, i.e., criminal records, urine toxicologies, treatment attendance, pay stubs. The project will therefore produce a revised instrument which will incorporate the strengths of the existing ASI (retaining its composite score items), yet meaningfully broadens it s assessments coverage (including cost items) and enhances its structural integrity. Training/instructional packages will be developed that will facilitate use of the instrument, including computerized scoring. Because of the widespread use of the ASI, the proposed revision should have important positive consequences for the field.